Question: $\dfrac{9}{12} - \dfrac{2}{5} = {?}$
$ = {\dfrac{9 \times 5}{12 \times 5}} - {\dfrac{2 \times 12}{5 \times 12}} $ $ = {\dfrac{45}{60}} - {\dfrac{24}{60}} $ $ = \dfrac{{45} - {24}}{60} $ $ = \dfrac{21}{60}$